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The NGRM500 Neutral Grounding Resistor Monitor detects grounding-resistor failures and ground faults. It is intended for use in high-resistance grounded transformers and generators used in commercial and industrial power systems. In these systems, the NGRM500 monitors:

  • Current through the neutral-grounding resistor (NGR)
  • Voltage between the star point of the transformer and ground (voltage drop across the NGR)
  • NGR failure (open and short), including failure of connections between neutral and ground

The NGRM500 can display the measured values, including current and voltage harmonics on the human machine interface (HMI). Users are able to select filters for ground-fault current and NGR voltage to prevent nuisance operation in noisy applications. A benefit to many users is the multilingual user interface that allows the comfort of reading values and programming in your native language.

It is a compact design with DIN rail mounting making it easy to retrofit into existing HRG applications or factory-install in new HRG packages. If customers prefer, they can easily program the relay via the built-in webserver. NGRM500’s can easily connect to a supervisory system with Modbus TCP/IP or RTU communications. Capabilities extend to 25 kV and 100 A.

The NGRM500 allows the user to meet Canadian requirements. It can be used to perform the functions required by Rule 10-302, Use of Impedance Grounded Systems, of the CE Code, C22.1-18, Section 10, Grounding and Bonding.


  • Determination of RNGR with passive and active measurement methods
  • Continuous monitoring of the RNGR even if the installation is de-energised;
  • Alarm or trip on ground fault
  • Monitoring of the current INGR
  • Monitoring of the voltage UNGR
  • Ethernet communication
  • Web server
  • Language selection (German, English GB and US, Spanish, French)
  • Test button (internal, external) with/without tripping
  • FFT analysis of the measuring signals
  • Pulser for manual ground fault location
  • Relay for detection of ground faults and resistor faults
  • Relay for shutdown of the installation after a configurable time
  • Can be combined with RCMS… for automatic shutdown of feeders
  • Graphical user interface
  • Wide supply voltage range
  • Range of use up to 2000 m AMSL
  • Fault/History memory
  • Analogue output of measured values (0…10 V, 4…20 mA, etc., selectable parameters)
  • Password protection
  • Tripping on RMS, fundamental component signal or harmonics
  • Detection of AC and DC ground faults

Downloads for LINETRAXX® NGRM500

CE Declarations of Conformity NGRM 83.0 KB 2022/08/12 06:17:2512.08.2022 06:17:25
Manuals NGRM…-Modbus 443.2 KB EN2022/06/09 10:47:4409.06.2022 10:47:44D00292
Technical Information How to Size an NGR (US) 424.0 KB EN2019/05/13 10:31:3513.05.2019 10:31:35
Quickstarts NGRM500/NGRM550 1.6 MB EN2022/06/09 10:52:1409.06.2022 10:52:14D00373
Manuals NGRM500/NGRM550 5.4 MB EN2022/06/09 10:48:1109.06.2022 10:48:11D00373
Technical Information NGRM500 Guideform Specification (US) 141.3 KB EN2020/04/30 18:55:2730.04.2020 18:55:27
Technical Information NGR Checklist (US) 245.3 KB EN2022/11/07 16:39:0207.11.2022 16:39:02
Technical Information Guideline on NGR/Safety Ground Monitoring 234.7 KB EN2019/09/20 13:52:3320.09.2019 13:52:33
Technical Information NGRM500 Retrofit Guide (US) 1.3 MB EN2021/02/10 20:59:2210.02.2021 20:59:22
Technical Information Guideline on NGRM Relay Testing 522.3 KB EN2021/10/26 18:41:5226.10.2021 18:41:52
Product Brochures HRG & LRG Systems (US) 5.2 MB EN2020/03/05 21:02:3305.03.2020 21:02:33
Flyers Neutral Grounding Resistor Monitors (US) 343.7 KB EN2020/03/23 17:32:0023.03.2020 17:32:00
Datasheets NGRM500/NGRM550 1.2 MB EN2022/06/09 10:54:4009.06.2022 10:54:40D00373
Flyers NGRM550 & NGRM750 630.6 KB EN2022/05/25 06:07:5225.05.2022 06:07:52

Optional Accessories for LINETRAXX® NGRM500

CD-series coupling device

TypeVoltage UsysArt. No.
CD1000400…690 VB98039010
CD1000-2400…1000 VB98039053
CD50001000…4200 VB98039011
CD144004300…14550 VB98039054
CD2500014551…25000 VB98039055

Measuring current transformer

TypeVoltage/CurrentArt. No.
W20AC up to 10 AB98080003
AC up to 25 AB98080010
CTUB103-CTBC35AC/DC up to 10 AB78120030
AC/DC up to 25 AB78120031

Voltage supply for measuring current transformers CTUB103…

Typemax. connected measuring current transformersArt. No.
STEP-PS/1 AC/24 DC/0.52B94053110
STEP-PS/1 AC/24 DC/1.757B94053111
STEP-PS/1 AC/24 DC/4.217B94053112


TypeSupply voltage U/ Frequency range HzArt. No.
NGRM500AC 48…240 V, 40…70 Hz
DC 48…240 V